Typecheck JS files for chrome://history

chrome/browser/resources/history/history_focus_manager.js

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 var FocusManager = cr.ui.FocusManager;
 
 /**
  * A history-specific FocusManager implementation, which ensures that elements
  * "background" pages (i.e., those in a dialog that is not the topmost overlay)
  * do not receive focus.
  * @constructor
+ * @extends {cr.ui.FocusManager}
  */
 function HistoryFocusManager() {
 }
 
 cr.addSingletonGetter(HistoryFocusManager);
 
 HistoryFocusManager.prototype = {
   __proto__: FocusManager.prototype,
 
   /** @override */
   getFocusParent: function() {
     return document.querySelector('#overlay .showing') ||
         document.querySelector('menu:not([hidden])') ||
         $('history-page');
   },
 };